Probing the Coordination Chemistry of [Zr₆BCl₁₂]⁺: A Cluster Especially Amenable to NMR Study

NMR spectroscopy is demonstrated to be a powerful analytical tool for the study of solvolysis and ligand-exchange chemistry of the [Zr6BCl12]+ cluster in acetonitrile, methanol, and pyridine. 11B NMR spectra for [(Zr6BCl12)Cl6-xLx]x-5 (L = CH3CN, CH3OH, and pyridine; x = 1−6) are reported. Exceedingly narrow 11B lines are generally observed for these clusters. Two-bond (2JP-Zr-B = 8.8 Hz) and three-bond coupling constants (3JP-O-Zr-B = 1.9 Hz) are observed for the cluster complexes [(Zr6BCl12)(PR3)6]+ and [(Zr6BCl12)(OPR3)xL6-x]+ (L = CH3CN and PR3), respectively, in both 11B and 31P NMR spectra. Spin−lattice relaxation times (T1's) for 11B were measured for several cluster complexes. Homoleptic species, [(Zr6BCl12)L6]+ (L = CH3CN, CH3OH, pyridine), exhibit very long times and that for [(Zr6BCl12)(NCCH3)6]+ is the longest ever measured (T1 = 108 s) for the 11B nucleus. A thermodynamic analysis of spectra for the [(Zr6BCl12)(CH3OH)6-x(py)x]+ (x = 0−5) system reveals that [Zr6BCl12]+ binds pyridine more strongly than methanol by about 3 kJ/mol. Crystallographic structural analyses of [(Zr6BCl12)Cl(py)5]·3CH3CN and [pyH]{cis-[(Zr6BCl12)Cl2(py)4]}·3py are also reported. The following parameters were determined for these two compounds: [(Zr6BCl12)Cl(py)5]·3CH3CN, orthorhombic, Pbcm, a = 13.4268(1) Å, b = 25.8258(1) Å, c = 14.5918(2) Å, Z = 4; [pyH]{cis-[(Zr6BCl12)Cl2(py)4]}·3py, monoclinic, C2/c, a = 14.5999(3) Å, b = 21.2298(5) Å, c = 19.8292(5) Å, β = 101.892(1)°, Z = 4.